A Microfluidic Single Molecule Free Solution Hydrodynamic Separation Platform Despite the power of modern methods such as microarrays, digital PCR, and deep sequencing, gel electrophoresis remains the workhorse of molecular biology. While high sizing resolution can be obtained using electrophoresis, dynamic range is limited, requiring specific assays tailored to small (PAGE), medium (slab agarose), or large DNA (PFGE). Furthermore, detection sensitivity is limited and quantification accuracy is poor, necessitating large sample volumes and DNA amounts. Capillary electrophoresis features increased sensitivity, fast analysis times, and reduced sample consumption but with increased complexity, cost, and the same limited sizing dynamic range. Single molecule free solution hydrodynamic separation (SML-FSHS) is an integrated technique for sized-based separation of DNA and quantification by single molecule counting that performs separation with only a buffer-filled microcapillary and pressure source. This method has a unique combination of wide dynamic range (100 bp - 27 kbp), high sizing resolution and near zero sample consumption (10 pL). Furthermore, it is among the most sensitive, amplification-free detection methods available, requiring only 10-23 moles of DNA for analysis and possessing quantitative accuracy that approaches the limits imposed by molecular shot noise. In this Phase I SHIFT proposal, a microfluidic SML-FSHS platform called PicoSep will be developed that surpasses the sizing performance, detection sensitivity, and speed of the previous microcapillary systems and any current DNA sizing method. This will be accomplished through: 1) the initial demonstration of a micro/nanofluidic device to enhance speed and resolution, 2) the novel incorporation electrokinetic sample stacking to further enhance concentration sensitivity, and 3) the development of a compact instrument platform to reduce cost and facilitate ease-of-use. This instrument will address the preconceptions that single molecule methods are bulky, expensive, and difficult. The unmatched sensitivity, wide dynamic range, and low sample consumption will make PicoSep an ideal detection platform for PCR-free, multiplexed biomarker assays in clinical diagnostics and cancer medicine.